The invention relates to rolls used in processing or manufacturing paper or other web-like materials, and specifically to a thermal roll used for heating or cooling a paper or other web. In particular, the roll is useful for impulse drying a paper web.
Various types of rolls are used during the manufacture and processing of paper and other web-like materials. For example, paper machines may include calender rolls, press rolls, drying cylinders, and Yankee cylinders. Each of these rolls performs some type of processing on the web. For example, a web may be heated or cooled.
One example of an apparatus used for heating the web is an impulse dryer, which rapidly supplies a large amount of heat to dry a fibrous web. An impulse dryer can include a roll having a cylindrical shell that is rotatably journaled at its axial ends and a stationary shaft located within the shell. It is known in the prior art to heat a roll by supplying a heated liquid such as oil or water within the space defined by the shell. For example, heated water can be supplied to one end of the shell of a roll and removed from the opposite end of the shell. Heat is transferred from the water through the shell and to the web.
A number of problems are presented by such a system. First, because the heated liquid cools as it flows through the shell, it has less capacity for heating the shell near the end through which it exits. This causes non-uniformities in heating across the length of the shell. Additionally, due to the large size of rolls, large volumes of liquid can be accommodated. However, the liquid is heavy, necessitating additional energy to rotate the shell. Energy is required to heat the volume of liquid, and changes in temperature may be achieved slowly. Also, a large volume of moving liquid can interfere with the movement of the shell. Alternatively, the shell may be only partially filled with liquid, and the remaining volume filled with air. The air is pressurized in order to force the liquid from the shell. However, the pressure creates additional stress on the components of the roll and presents a danger to both nearby workers and equipment. Heating is less effective because the air in the shell is a poorer heat transfer agent than the liquid. Also, in a partially filled shell, gravity causes the heating liquid to collect at the bottom of the shell, tending to reduce the effectiveness of heating at the top of the shell.
Thus, there exists a need for a roll for transferring heat to or from a web. The roll should allow for effective and efficient heating by enabling high heat transfer rates to the web and minimizing heat losses to the working environment. Heat transfer should be uniform across the length of the roll. The roll should allow quick and efficient changes to the temperature of the heating liquid. Also, dangers associated with complex pressurized systems should be minimized. Finally, the roll should be adaptable for use as different types of rolls, such as calender rolls, press rolls, drying cylinders, and Yankee cylinders.
The present invention provides an improved thermal roll for heating or cooling a web that solves these deficiencies in the prior art. The thermal roll includes a reduced volume of heat exchange fluid, which completely fills an annular space adjacent to a rotatable outer shell that supports the fibrous web. The heat exchange fluid is passed to the annular space through a plurality of connection pipes that are fed from a main supply pipe. As a result of the heat exchange fluid filling the annular space, heat is effectively exchanged to or from the fibrous web through the rotatable outer shell.
The roll of the present invention includes a rotatable outer shell and a stationary inner shell within the outer shell. The rotatable outer shell has an outer surface and an inner surface and extends from a first head to a second head. The rotatable outer shell is positioned to rotate about a longitudinal axis and support the web. The stationary inner shell also has an outer surface and an inner surface. The outer surface of the stationary inner shell and the inner surface of the rotatable outer shell define an annular space. The stationary inner shell extends from a first end to a second end and defines a plurality of inner shell openings. The thermal roll includes a main supply pipe that is positioned within the stationary inner shell and extends from the first end of the stationary inner shell longitudinally toward the second end of the stationary inner shell. Additionally, the thermal roll includes a plurality of connection pipes that connect the main supply pipe to the plurality of inner shell openings. The annular space is completely filled with the heat exchange fluid and heat is effectively exchanged by the roll through the rotatable outer shell.
According to one embodiment of the present invention, the main supply pipe extends from the first head of the rotatable outer shell longitudinally to the second head of the rotatable outer shell. The main supply pipe has an inlet located at one of the first or second heads of the rotatable outer shell, and the main supply pipe has an outlet located at the other of the first or second heads of the rotatable outer shell. In another embodiment, the main supply pipe has an inlet and an outlet, and both the inlet and the outlet of the main supply pipe are located at the same one of either the first or second heads of the rotatable outer shell. In another embodiment of the present invention, the main supply pipe is directly connected to each of the connection pipes.
The annular space encompasses a perimeter of the outer surface of the inner shell. In one embodiment, the inner surface of the outer shell is located less than 40 millimeters from the outer surface of the inner shell. The annular space may extend from the first end of the stationary inner shell to the second end of the stationary inner shell.
According to another embodiment, the connection pipes comprise flexible hose, and the stationary inner shell defines an inner body space encompassing the connection pipes.
The thermal roll also includes a main evacuation pipe. The main evacuation pipe is positioned within the stationary inner shell and extends from the first end of the stationary inner shell longitudinally in a direction toward the second end of the stationary inner shell. The thermal roll can further include a plurality of evacuation connection pipes. The inner shell includes a second plurality of inner shell openings, and the evacuation connection pipes connect the main evacuation pipe to the second plurality of inner shell openings.
The thermal roll according to one embodiment also includes an expansion tank that is fluidly connected to the annular space. The expansion tank contains quantities of both the heat exchange fluid and a compressed gas.
The thermal roll also includes a temperature regulating device for changing the temperature of the heat exchange fluid. The temperature regulating device can be externally located or within both the outer shell and the stationary inner shell.
The present invention also provides a closed circulation system for thermally treating a web during papermaking. The circulation system, which is capable of being fluidly closed, includes an annular space defined by an inner surface of a rotatable outer shell and an outer surface of a stationary inner shell. A main supply pipe is positioned within the stationary inner shell and fluidly connected to the annular space via a plurality of connection pipes. An expansion tank, located outside the rotatable outer shell, is fluidly connected to the annular space and capable of containing quantities of both the heat exchange fluid and a compressed gas for adjustment of a flow of a heat exchange fluid within the circulation system.
Additionally, the present invention provides a method of heating or cooling a roll for processing a web. The method includes providing a rotatable outer shell and a stationary inner shell located within the rotatable outer shell to define an annular space between an inner surface of the rotatable outer shell and an outer surface of the stationary inner shell. The method also includes completely filling the annular space with a heat exchange fluid and sealing the annular space so that there is no air contained within it. The rotatable outer shell is rotated relative to the stationary inner shell to provide circulation of the heat exchange fluid from a main supply pipe through a plurality of connection pipes directly and simultaneously to a plurality of locations on the inner surface of the rotatable outer shell within the annular space. The heat exchange fluid is evacuated from the annular space to a temperature regulation device where it is heated or cooled. The heat exchange fluid is then re-circulated to the annular space.
Thus, the present invention provides a roll for efficiently transferring heat to or from a web. The roll includes an annular gap that is completely filled with a relatively low volume of heat exchange fluid, thus enabling high heat transfer rates to the web. The low volume also allows the temperature of the heat exchange fluid to be changed quickly and efficiently. Dangers associated with complex pressurized systems are minimized and heat transfer across the length of the roll can be uniform. Additionally, the roll of the present invention is adaptable for use as various types of rolls, such as calender rolls, press rolls, drying cylinders, and Yankee cylinders.